WO2004103520A2

WO2004103520A2 - Settling tank for treatment of waste effluents

Info

Publication number: WO2004103520A2
Application number: PCT/FR2004/001269
Authority: WO
Inventors: Hervé Philip; Siegfried Maunoir
Original assignee: Ergalia
Priority date: 2003-05-21
Filing date: 2004-05-21
Publication date: 2004-12-02
Also published as: FR2855070B1; WO2004103520A3; FR2855070A1; EP1484095A2; EP1484095A3; DE602004011424D1; EP1484095B1; ATE384565T1

Abstract

The invention relates to a settling tank which is intended for the treatment of waste effluents. The inventive settling tank comprises a tank (101) into which waste effluents are introduced. Once said effluents have settled, they are discharged downstream, with the sludge resulting from the settling process also being discharged. The settling area in the tank comprises a suitable friction coefficient and surface roughness. The aforementioned settling area is formed by the upper face of the panels which are disposed in parallel to the flow of effluents and which are inclined in relation to the vertical, in a plane that is transverse to the flow. The settling tank comprises at least one first assembly of panels (114) which are inclined at an angle (a) and a second assembly of panels (114') which are inclined at an angle (ß), a discharge conduit (117) being provided between said panels such that the sludge collected thereon can fall to the base of the tank. The invention also relates to a treatment plant comprising one such settling tank.

Description

Clarifier for the treatment of effluents worn

The invention relates to a decanter intended for the treatment of spent effluents, as well as a purification station comprising in particular such a decanter.

In general, the raw effluents treated in a treatment plant, for example domestic effluents, are first directed to a decanter, so as to be discharged from a large proportion of the suspended solids which it contains. Is thus obtained at the outlet of the decanter on the one hand decanted effluents, and on the other hand sludge, these two fractions then undergoing separately a number of additional treatments.

Compact decanting systems have been developed in the form of tanks, in which the effective decanting surface is defined by one or a plurality of inclined panels, by the arrangement of bundles of tubes or by honeycomb structures.

These compact decantation systems can in particular, but not exclusively, be used in the case of small communities, or on rugged and / or difficult to access sites.

Document FR 2 699 421 in particular discloses a decanter comprising a plurality of flat panels, arranged in the tank transversely to the flow which would be that of the effluents from the inlet to the outlet, in the absence of such panels. In addition, the panels are inclined relative to the vertical from bottom to top, from upstream to downstream.

The effluents are introduced from the bottom of the tank, through a plurality of inlets, circulate along two successive panels from bottom to top and then from top to bottom, and are discharged through the outlet. The introduction of effluents from the bottom of the tank, under the panels, generally poses hydraulic problems, since the flow of the effluent cannot simply intervene by gravity. In particular, it is often necessary to set up a tank buffer fitted with a pumping system allowing precise entry of spent effluents in the lower part of the tank.

In addition, such an arrangement allows the installation of only one stage of panels, and therefore limits the available settling surface.

Document EP 0 354 349 also discloses a device for the treatment of spent effluents comprising a settling compartment provided with a plurality of panels arranged parallel and obliquely one above the other, these panels extending parallel to the flow direction of effluents. This device has many disadvantages.

First of all, the panels all have the same inclination, which does not lead to optimal settling of the effluents.

In addition, the sludge discharged in the lower part of the panels is distributed over the entire horizontal section of the compartment. In order to direct them to a desired area at the bottom of the compartment, in particular for their recovery, it is necessary to provide a tank, the lower part of which has the shape of a funnel. This type of panel cannot therefore be used in a completely satisfactory manner with any tank structure.

Finally, part of the sludge contained in the effluents cannot fall to the bottom of the tank, due to the arrangement of certain panels whose slope directs the sludge towards the side walls of the compartment. There is then an accumulation of sludge against these walls, which reduces the settling performance of such a compartment and requires regular maintenance operations.

To overcome these drawbacks, the invention provides a decanter intended for the treatment of spent effluents containing sludge, of the type comprising: - a tank having a bottom and having, relative to the direction of flow of the effluents, an upstream part in which leads to a conduit supply of used effluents and a downstream part into which opens a discharge pipe for the settled effluents;

- a settling surface disposed in the tank, formed by the upper face of at least one settling panel, said panel having a mean plane substantially parallel to the direction of flow of the effluents and inclined, in a plane transverse to the flow effluents, and with respect to the orthogonal projection of the vertical in said transverse plane, by an angle (α, β);

- means for evacuating sludge from decantation out of the tank; the decanter comprising at least a first set of at least one decantation panel inclined at a first angle (α) between 15 ° and 60 ° and at least a second set of at least one decantation panel inclined at a second angle (β) between 15 ° and 60 °, the angles (α, β), the surface condition and the coefficient of friction of the panels being chosen so that, when the effluents flow into the tank, the sludge settle on the settling surface and then slide towards the bottom of the tank, at least one sludge evacuation passage being provided between the panels of the two assemblies, so as to allow the sludge collected on the upper faces of the panels to fall by gravity on the bottom of the tank

The possibility of moving the sludge by sliding in two different directions towards the bottom of the tank increases the performance of the settling.

The first angle α and the second angle β are different. According to a first possible embodiment, α and β have different absolute values. According to a second possible embodiment, α and β have the same absolute value, the panels then being inclined with opposite orientations relative to the vertical.

According to a possible embodiment, the first and second assemblies are located on either side of a vertical separation plane and parallel to the direction of flow of the effluents, the panels of an assembly being inclined up and down towards said plane of seperation. In this way, the sludge is led to the bottom of the tank, in an area provided for this purpose. Thus, on the one hand, their recovery is facilitated, in particular via an orifice and a discharge duct, which is particularly advantageous in the case where the sludge is then conveyed to a subsequent treatment unit. On the other hand, the risk of accumulation of sludge near the side wall of the tank is considerably reduced.

According to another possible embodiment, the first and second assemblies are located on either side of a vertical separation plane and parallel to the direction of flow of the effluents, the panels of an assembly being inclined from bottom to top towards said separation plan.

The separation plane is for example the median longitudinal vertical plane of the tank. At least one of the panels of the first set can be the image of one of the panels of the second set by a symmetry with respect to the separation plane.

According to a possible embodiment, at least one assembly comprises at least two panels whose mean planes are substantially parallel, said panels being substantially superimposed and spaced vertically from one another.

Such a settling surface, called a lamellar surface, makes it possible to obtain optimal settling performance. Indeed, the superposition of the panels leads to an increase in the settling area without a substantial increase in the volume of the tank. In addition, before the installation of the tank on the treatment site, it is possible to adapt the decantation surface as a function of the effluent inlet flow, by increasing or decreasing the number of superimposed panels and / or by increasing or decreasing their length.

According to a possible embodiment, at least one assembly comprises at least a first, a second and a third panel whose mean planes are substantially parallel, said first, second and third panels being substantially superimposed in this order and spaced vertically from each other, the vertical spacing between the median planes of the first and second panels being substantially identical to the vertical spacing between the median planes of the second and third panels.

For example, at least one panel is solid and substantially plane.

The decanter may comprise two sets symmetrical with respect to the median longitudinal vertical plane of the tank, each set each comprising between three and seven substantially planar panels, superimposed and spaced vertically from each other, said panels being inclined at an angle. between 40 and 50 °, from top to bottom towards said median longitudinal vertical plane of the tank.

According to a second aspect, the invention relates to a treatment plant comprising at least one such decanter.

The other characteristics of the invention result from the following description of embodiments, description made with reference to the appended figures in which:

- Figure 1 is a schematic cross-sectional view of a settling tank according to the invention, comprising panels forming a settling surface;

- Figure 2 is a sectional view along line AA of the decanter of Figure 1;

- Figure 3 is a sectional view of the decanter of Figure 1, along the line BB of Figure 2;

- Figures 4a to 4h are schematic representations of different possible embodiments of the decanter of Figure 1, with regard to the panels;

FIG. 5 is a schematic representation of a purification station according to the invention, comprising in particular a decanter, a filter or a filtration installation, and an anaerobic sludge digester, illustrating in in addition to the steps of a process for treating used effluents in said treatment plant;

- Figure 6 is a schematic view in longitudinal vertical section of a filter provided in the treatment plant, according to a possible embodiment;

- Figure 7 is a schematic sectional view, along a vertical longitudinal median plane, of a digester provided in the treatment plant, according to a possible embodiment;

- Figure 8 is a schematic perspective view of the digester of Figure 7, seen in the same section.

First of all, reference is made to FIGS. 1 to 3 which represent a settling tank 100 according to the invention, intended for the treatment of spent effluents.

The decanter 100 comprises a tank 101 of generally substantially cylindrical shape with an axis 102, with respect to which the term "longitudinal" is defined. The tank 101 is closed with the exception of four openings as will be seen below. The tank is for example made by rotational molding or injection of a plastic material possibly reinforced with glass fibers. For example, it can have a volume of 30 m ³ .

The tank 101 is buried, and positioned so that the axis 102 is substantially horizontal. It comprises a substantially cylindrical side wall defining a bottom 103 and an upper wall 104, as well as an upstream end wall 105 and a downstream end wall 106.

In the upper part of the upstream wall 105 is formed an opening allowing the entry into the decanter 100 of the effluents to be decanted, by a supply conduit 107. The supply conduit 107 extends inside the tank 101 substantially parallel to the axis 102 over a length of the order of 50 cm for example, then vertically downwards over a neighboring length, and finally substantially parallel to the axis 102, towards the upstream wall 105, so as to form inside the tank 101 an elbow 108 open upstream. The elbow 108 aims to reduce the turbulence formed by the supply of effluents and likely to interfere with settling.

In the upper part of the downstream wall 106, at a distance from the bottom 103 slightly less than the distance between the bottom 103 and the inlet opening, there is an opening allowing the evacuation of the decanted effluents from the decanter 100, by a exhaust 109.

The upper wall 104 of the tank 101 may, for its part, include a inspection hatch 110.

Finally, in the bottom 103 of the tank can be formed an orifice for discharging the sludge from the settling, said orifice being connected to a discharge conduit 111 for said sludge, cut-off means 112 for said discharge conduit 111 being provided. As a variant, the evacuation means may include pressure pumps immersed in the tank 101 or suction pipes rising above the tank 101 and connected to a suction pump.

The tank also has a plane of symmetry 113, vertical, longitudinal and median.

The decanter 100 has a decantation surface formed by the upper face of panels 114 arranged inside the tank 101. Whatever the embodiment considered, the mean plane of a panel 114 is substantially parallel to the direction of effluent flow, here substantially parallel to the horizontal axis 102, and inclined, in projection in a vertical plane, at an angle α relative to the vertical, between 15 and 60 ° (see Figure 3).

A panel is for example made up of a substantially flat and rectangular metal plate, provided to allow the sludge introduced into the tank 101 to settle on the upper face of said plate and then slide on said upper face towards the bottom 103 of the tank. 101. In the embodiment of FIGS. 1 to 3, the panels 114 are arranged in two sets, symmetrically with respect to the vertical plane 113.

The first set (on the left in FIGS. 1 and 3) comprises five panels 114a to 114e substantially parallel, superimposed vertically, and spaced from each other by a substantially constant distance. The vertical spacing L1 between two successive panels 114 is between 20 and 50 cm, for example of the order of 30 cm. As a variant, the vertical spacing between two successive panels could be variable, depending on the vertical position of the panels considered in the tank, that is to say their depth below the level of effluents.

The panels 114a to 114e are inclined from top to bottom from the substantially vertical side wall of the tank 101 towards the vertical plane 113, at an angle α between 40 and 50 °, in particular of the order of 45 °.

The first set of panels 114 is housed in a substantially rectangular contour space, in cross-section view (see FIG. 3). Therefore, and given their inclination, the panels 114 have different widths I depending on their distance from the bottom 103 of the tank 101, the width I of the panels 114 being all the smaller as one s' away from the medial panel 114c. On the other hand, their lengths L (parallel to the flow of the effluents) are substantially equal, and for example close to 3 m.

The superimposition of the panels makes it possible to considerably increase the settling surface in the same tank volume. Thus, in the embodiment shown in Figures 1 to 3, with an angle α close to 45 °, the decantation surface for 1 linear meter of panel is as follows:

The horizontal distance L2 between the vertical side wall of the tank 101 and the first set of panels is of the order of 10 cm. Thus, a space is created which is large enough to allow the passage of suspended matter contained in the spent effluents. Furthermore, the first set of panels is also separated horizontally from the vertical plane 113, as will be seen below.

The lower end of the first set of panels is located at a vertical height H above the bottom 103 of the tank 101. This height H, for example of the order of 30 cm, makes it possible to provide a space 115 above bottom 103 for the accumulation of sludge from decantation.

As for the upper end of the first set of panels, it is located at a distance d below the level 116 of the effluents inside the tank 101. The distance d is for example of the order of 30 cm.

The second set (on the right in FIGS. 1 and 3) is symmetrical with the first with respect to the vertical plane 113, and comprises five panels 114'a to 114'e. The horizontal spacing L3 between the first and second sets of panels 114, 114 ′ is between 20 and 50 cm, and in particular close to 30 cm. The space 117 thus formed between the two sets of panels 114, 114 ′ allows the sludge collected on the panels to fall towards the bottom 103 of the tank 101 without falling on the lower panels, the sludge being further directed and collected in the zone center of the bottom 103 of the tank 101.

Means 118 for supporting and fixing the panels 114, 114 'to the tank 101 are arranged in the vicinity of the upstream and downstream ends of said panels. In the embodiment shown, the support means 118 comprise two substantially vertical rods and three substantially horizontal rods on which are fixed the panels 114, 114 '. Intermediate support means can also be provided for questions of mechanical strength of the support means. In this case, the panels 114, 114 ′ can be produced in two parts adjacent to the vicinity of the intermediate support means.

We will now describe the operation mode of the settling tank 100.

The spent effluents, containing suspended matter which will be recovered in the form of sludge, are introduced into the decanter 100 through the supply conduit 107 and flow into the tank 101 towards the evacuation conduit 109, substantially longitudinally. There is maintained in the tank 101 an effluent level 116 as shown in FIGS. 1 and 3. The level 116 of effluents is substantially flush with the lower end of the discharge conduit 109.

During the flow of the effluents in the tank 101, taking into account the difference in density between the sludge and the effluent, the sludge is deposited by gravity on the decantation surface - the panels 114, 114 '- then slides over this surface , in particular under the thrust action of the sludge which subsequently falls on the settling surface, as the flow and settling continue.

By gravity, the sludge collected on the panels 114, 114 'then falls to the bottom 103 of the tank 101.

In order to allow this settling, the settling surface formed by the panels 114, 114 'has a surface condition and a coefficient of friction adapted to the following different parameters: nature of the effluents and sludge introduced into the tank, angle α of inclination panels, effluent supply rate. A person skilled in the art knows how to choose the panels which are suitable as a function of these various parameters in order to obtain satisfactory settling. The decanted effluents freed at least in part of the suspended matter are evacuated through the evacuation conduit 109 and conveyed, if necessary, to another treatment unit. The sludge can be removed by simple gravity or using suitable pumping means.

A siphonic wall 119 is provided inside the tank 101 upstream and facing the discharge pipe 109 of the decanted effluents, so as to allow the retention of the floating materials inside the tank and avoid their evacuation with the settled effluents. The siphoic wall 119 comprises: - on the one hand a substantially vertical part extending from the upper wall 104 of the tank 101 and substantially up to the axis 102, said vertical part having at its lower part, below the level 116 effluent, an opening 120 for passage of effluent; - on the other hand, a part extending obliquely from the lower end of the vertical part towards the downstream wall 106 of the tank 101.

As for the sludge from the decantation, it is evacuated through the evacuation conduit 111 and conveyed, if necessary, to another treatment unit. As a variant, the bottom 103 of the tank may not include a sludge discharge pipe 111, the sludge then being temporarily stored in the tank 101, the latter being periodically emptied via the inspection hatch 110 or the orifice discharge provided in the bottom.

Such a decanter 100 has many advantages.

First of all, the decantation efficiency of such a decanter can reach 90%.

In addition, the decanter is in the form of a prefabricated tank, which can be installed even on sites that are difficult to access. Its establishment does not require any heavy civil engineering type infrastructure. As a result, the settling tank makes it possible in particular, but not exclusively, to respond advantageously to the problem of the primary treatment of spent effluents for small communities, a problem to which previously existing solutions could not simply respond. In addition, this type of decanter makes it possible to easily increase the decantation surface by increasing the number of superimposed panels and / or by increasing the length of the panels, without modifying the volume of the tank, so as to be able to cover the whole range of peak flows generated by the populations concerned. The invention thus makes it possible to multiply the decantation capacity by 3 for simple tanks (when the sludge is temporarily stored at the bottom of the tank), by 15 to 34 if the sludge is removed and treated separately.

A decantation installation can be provided comprising several decanters 100 in parallel, so as to increase the decantation capacity, but also to optimize the possible decanting and emptying operations of the decanters.

Other possible arrangements of the decanter panels are shown schematically in Figures 4a to 4h.

In FIG. 4a, the decanter comprises a first panel 114 (on the left) inclined at an angle α from top to bottom and towards a longitudinal but non-median vertical plane P of the tank 101. A second panel 114 '(on the right) is inclined by an angle β different from α, from top to bottom and towards the plane P.

In FIG. 4b, the first panel 114 is inclined at an angle α from bottom to top towards the plane P, the second panel 114 'being inclined at an angle β other than α, from bottom to top towards the plane P.

The embodiment of FIG. 4c is similar to that of FIG. 4a, the plane P being coincident with the median plane 113, the panels 114, 114 'being inclined by the same angle α.

The decanter can also include three sets of panels inclined alternately so as to form a zig-zag (FIG. 4d). In FIG. 4e, similar to FIG. 4c, the first panel is replaced by a set of five superimposed and substantially parallel panels 114a to 114e (as in the case of FIG. 3), while the second panel 114 'is always unique .

As a variant, the panels 114a to 114e may not be parallel to one another, as shown in FIG. 4f. The left part of the tank then comprises a group of five sets of panels (a set of panels being defined by a tilting direction).

Finally, the tank 101 may include first, second, third and fourth sets of panels 114, the panels being arranged so as to substantially form a W or, conversely, an M. The assemblies may each comprise a single panel 114 (Figure 4g) or all or part of the assemblies may comprise a plurality of superimposed panels substantially parallel. In the case of FIG. 4h, the first and second sets each comprise five superposed panels, while the third and fourth sets each comprise a single panel.

Of course, other arrangements can be considered.

According to one possible embodiment, the decanter 100 comprises, with respect to the direction of flow of the effluents, at least a first and a second series of panels 114, 114 ′, the second series being located downstream from the first series, said series each comprising at least first and second sets of at least one panel. Within each series, the panels can be arranged according to one of the embodiments of FIGS. 4a to 4h, or according to mixed embodiments.

The two series are for example located on either side of a vertical plane orthogonal to the axis 102 of the tank 101. The first series, located upstream, may include panels in number, inclination and / or state of surface such that the settling performance is average. The second series, by which then pass the effluents, may in turn include panels arranged to allow a much more efficient settling. Thus, the first series aims to retain particles of larger dimensions, while the second series allows to settle the finer particles. Such a decanter 100 further improves the extraction of sludge.

We will now describe, with reference to FIG. 5, a treatment plant 46 for used effluents.

The raw effluents are brought via a supply conduit 107 at the inlet of the primary settling tank 100, so as to be rid of a large proportion of their suspended matter.

The discharge pipe 109 of the decanted effluents is connected to the inlet of the effluents to be filtered from a filter 1 or from a filtration installation 34 comprising several filters 1 operating in parallel, via a supply pipe 4.

The sludge from the primary decantation is discharged to a digester 200, via the evacuation means, for example by the evacuation conduit 111, connected to a supply conduit 207 for fresh sludge from an anaerobic sludge digester 200 .

The digester 200 comprises a discharge pipe 209 for the effluents connected to the supply inlet for effluents to be decanted from the primary settling tank 100, as well as a discharge outlet for the digested sludge connected, via a discharge pipe 212, to the input of a thickener 48.

The thickener 48 has an outlet 49 for the residual water connected to the inlet for the supply of effluents to be decanted from the primary decanter 100, possibly via the discharge pipe 209 for the effluents from the digester 200.

The thickener 48 also has an outlet 50 for thickened sludge. This sludge can be subjected to appropriate conditioning and treatment with a view to their use, especially for soil improvement. They can also be sent to a landfill or an incineration unit.

The effluents filtered by the filter 1, or the filtration installation 34, are evacuated by an evacuation duct 15. In the case where the filter 1 is able to retain the suspended solids contained in the effluents to be filtered, the effluents filtered are rejected directly. In the opposite case, the filtered effluents are directed to the inlet of a secondary decanter 51.

The filter 1 also includes racking outlets allowing the evacuation of the biomass by racking pipes 24, these can be connected either to the inlet of the secondary settling tank 51, or, when the station does not include a secondary settling tank , at the inlet for the supply of effluents to be decanted from the primary settling tank 100 or at the fresh mud supply inlet for the digester 200.

The secondary settling tank 51 includes means for evacuating the sludge from the settling, connected either to the inlet for the supply of effluents to be settled from the primary settling tank 100, via a discharge pipe 52, possibly opening into the pipe 209, either at the feed inlet for fresh sludge from the digester 200. Part of this sludge can also be sent back to the head of the filter 1 to maintain the biomass at a desired level.

In addition, the secondary settling tank 51 has a discharge pipe 53 for the decanted effluents.

In one possible embodiment, shown in FIG. 6, the filter 1 comprises, according to a general definition, a reactor 2 in which the flow of effluents to be filtered is intended to flow from bottom to top, said reactor 2 comprising: - in part low, an inlet 3 of the effluents to be filtered and an inlet 6 of oxygenated gas;

- And, in the upper part, an outlet 14 for the filtered effluents;

- filtering means 18 comprising layers of particles of a solid material forming supports and a biomass hung on the surface of said supports, said filtering means 18 having a density lower than the density of the effluents to be filtered and being interposed between the inlet 3 of the effluents to be filtered and the outlet 14 of the filtered effluents.

The reactor 2 is subdivided into at least three superimposed compartments forming stages by means of at least two walls 19a, 19b, 19c provided with openings, said openings being arranged to retain the filtering means 18, so as to form in the reactor: - at least two filter stages 20a, 20b, 20c; and an upper outlet stage 17, the outlet 14 of the filtered effluents opening into the upper outlet stage 17.

Each filtration stage 20a, 20b, 20c is provided with a layer of its own filtering means 18 and comprises, in the lower part, a withdrawal outlet 22a, 22b, 22c for the excess biomass, the quantity and density of the filtering means 18 in each filtration stage 20a, 20b, 20c being such that, in withdrawal mode, the lower part of at least the lower stage or stages 20a, 20b into which the withdrawal outlet 22a, 22b opens is free from filtering means, to allow the recovery of excess biomass.

The reactor 2 defines a main axis X vertically oriented. The inlet 3 of the effluents to be filtered is connected to a supply duct 4 provided with a valve 5, and the inlet 6 of oxygenated gas is connected to a supply duct 7 provided with a valve 8. According to a embodiment, the two inlets 3, 6 are provided in the bottom wall 9 of the reactor 2 and open into an inlet compartment 10 delimited by a part of the side wall 11 of the reactor, and by an internal top wall 12 permeable to effluents and oxyfuel.

The outlet 14 of the filtered effluents is connected to an evacuation pipe 15 provided with a valve 16, and opens into an upper outlet stage 17 of the reactor.

The reactor 2 is subdivided into superimposed compartments forming filtration stages, by grids 19a, 19b, 19c, the upper outlet stage 17, formed between the upper wall 21 of the reactor and the upper wall 19c disposed opposite, being free of filtering means.

Each filtration stage 20a, 20b, 20c comprises in the lower part a withdrawal outlet 22a, 22b, 22c of the excess biomass, connected to a withdrawal conduit 24 provided with a valve 25. A recovery compartment 23a, 23b, 23c said excess biomass may be provided.

The filtering means 18 are provided to float, at least in certain compartments, in racking mode, so as to form a free bottom space 31 free of filtering means. Grids 19d, 19e, 19f make it possible to retain the filtering means 18. A means 26 for detecting the amount of excess biomass can also be provided.

The filter 1 may include means 27 for recirculating the filtered effluents, comprising a conduit 28 associated with a pump 29, for additional treatment of at least a portion of the filtered effluents.

During the filtration phase, the effluents and the gas flow upwardly through the various filtration stages. The filtered effluents are discharged through line 15, and the biomass remains on the supports. The supply of effluents and / or gas is continuous or discontinuous.

During the washing phase, the excess biomass of the chosen stage is recovered by the corresponding withdrawal conduit 24 by downward flow of the effluents contained in the reactor 2.

According to a possible embodiment, represented in FIGS. 7 and 8, the digester 200 comprises, according to a general definition, a tank 201 having a substantially horizontal bottom 203, a supply pipe 207 for the tank with fresh sludge, a supply pipe 209 evacuation of effluents from the vessel, and discharge means 212 of the digested sludge from the tank, said tank having at least one wall 213a, 213b, 213c transverse to the effluent flow, the wall defining an upstream compartment 218a, 218b, 218c and a downstream compartment 218b, 218c, 218d, so that the tank has a first upstream compartment 218a, into which the supply duct 207 fresh sludge, and a last downstream compartment 218d, into which the discharge pipe 209 effluents. The wall 213a, 213b, 213c has, at its lower part, a communication opening

216 from the upstream compartment to the downstream compartment, so as to allow the passage of sludge and the flow of effluents, above and through the layer of sludge maintained at the bottom of the tank, in a substantially horizontal manner from the first upstream compartment 218a to the last downstream compartment 218d.

The tank 201, substantially cylindrical or of substantially rectangular vertical section, positioned so that its axis 202 is horizontal, is closed, with the exception of the following openings: - an inlet opening, formed in the upstream wall 205, connected to the supply line 207 with fresh sludge which forms an elbow 208;

- an effluent discharge opening, formed in the downstream wall 206, connected to the discharge conduit 209 forming a siphonic outlet 210;

- an outlet for digested sludge, in the bottom 203, connected to an outlet conduit 212;

- an inspection hatch 211 provided in the upper wall 204.

The digester 200 has three transverse walls respectively upstream 213a, intermediate 213b, and downstream 213c, having an annular contour 214 matching the interior shape of the tank 201 and an upper edge 215 horizontal. The height of the walls is less than the diameter of the tank, and for example of the order of 30 cm. In the lower part of each wall 213a, b, c is formed a communication opening 216 having an upper edge

217 ring finger.

The tank 201 is thus divided longitudinally into four compartments 218a, 218b, 218c, 218d. The walls make it possible to retain in each compartment the sludge formed by agglomeration of the suspended matter, while excess floating material can pass by overflowing from an upstream compartment to a downstream compartment, or even the reverse.

The fresh sludge introduced into the digester 200 has a dry matter concentration of less than 25 g / l. They are deposited on the bottom of the tank, in the form of a thin layer, for example less than 0.5 m. A level 219 of effluents is maintained in the tank 201. The sludge is gradually degraded and liquefied. They then pass into successive compartments through the communication openings 216. The effluents flow parallel to the axis 202, taking with them the soluble products resulting from the digestion of the sludge.

Claims

1. Decanter intended for the treatment of spent effluents containing sludge, of the type comprising: - a tank (101) having a bottom (103) and having, with respect to the direction of flow of the effluents, an upstream part into which a supply pipe (107) for spent effluents and a downstream part into which a discharge pipe (109) for decanted effluents opens;

- a settling surface disposed in the tank (101), formed by the upper face of at least one settling panel (114, 114 '), said panel having a mean plane substantially parallel to the direction of flow of the effluents and inclined , in a plane transverse to the flow of effluents, and with respect to the orthogonal projection of the vertical in said transverse plane, by an angle (α, β); - Evacuation means (111) of the sludge from the settling out of the tank (101); characterized in that it comprises at least a first set of at least one panel (1 14, 114a, 114b, 114c, 1 14d, 1 14e) of settling tank inclined at a first angle (α) between 15 ° and 60 °, and at least a second set of at least one panel (1 14 ', 114'a, 1 14'b, 1 14'c,

1 14'd, 114'e) decantation inclined at a second angle (β) between 15 ° and 60 °, the angles (α, β), the surface condition and the coefficient of friction of the panels being chosen from so that, during the flow of effluents into the tank, the sludge is deposited on the settling surface and then slides towards the bottom of the tank, at least one evacuation passage (11-17) of the sludge being provided between the panels of the two assemblies, so as to allow the sludge collected on the upper faces of the panels to fall by gravity onto the bottom (103) of the tank (101).

Decanter according to claim 1, characterized in that the first and second sets are situated on either side of a separation plane (113, P) vertical and parallel to the direction of flow of the effluents, the panels (114, 114 ') of an assembly being inclined up and down towards said separation plane.

3. Decanter according to claim 1, characterized in that the first and second sets are located on either side of a separation plane

(113, P) vertical and parallel to the direction of flow of the effluents, the panels (114, 114 ') of an assembly being inclined from bottom to top towards said separation plane.

4. Decanter according to claim 2 or 3, characterized in that the separation plane is the median longitudinal vertical plane (113) of the tank.

5. Decanter according to one of claims 1 to 4, characterized in that at least one of the panels (114) of the first set is the image of one of the panels (114 ') of the second set by a symmetry with respect to the separation plane (113, P).

6. Decanter according to one of claims 1 to 5, characterized in that it comprises a third set of at least one panel and a fourth set of at least one panel, the panels (114, 114 ') of the first , second, third and fourth sets being arranged so as to form substantially a W or an M.

7. Decanter according to one of claims 1 to 6, characterized in that the sets of panels are spaced by a transverse distance between 20 and 50 cm.

8. Decanter according to one of claims 1 to 7, characterized in that at least one assembly comprises at least two panels (114a, 114b, 114c, 114d, 114e, 114'a, 114'b, 114'c, 114'd, 114'e) whose mean planes are substantially parallel, said panels being substantially superimposed and spaced vertically from one another.

9. Decanter according to claim 8, characterized in that the vertical spacing (L1) between the median planes of two successive panels is between 20 and 50 cm.

10. Decanter according to one of claims 1 to 9, characterized in that at least one assembly comprises at least a first, a second and a third panel whose mean planes are substantially parallel, said first, second and third panels being substantially superposed in this order and vertically spaced from one another, the spacing between the vertical median planes of the first and second panels being substantially identical to the vertical distance between the median planes of the second and third panels.

1 1. Decanter according to one of claims 1 to 10, characterized in that at least one panel (114, 114 ') is solid and substantially planar.

12. Decanter according to one of claims 1 to 11, characterized in that the angle (α, β) of inclination of the panels is between 30 ° and 60 °.

13. Decanter according to one of claims 1 to 12, characterized in that the angle (α, β) of inclination of the panels is between 40 ° and 50 °.

14. Settling tank according to one of claims 1 to 13, characterized in that it comprises two assemblies symmetrical with respect to the median longitudinal vertical plane of the tank, each set each having between three and seven panels (1 14, 114 ') substantially planar, superimposed and spaced vertically from one another, said panels being inclined at an angle between 40 and 50 °, from top to bottom towards said median longitudinal vertical plane (113) of the tank (101).

15. Decanter according to one of claims 1 to 14, characterized in that the panels (1 14, 1 14 ') are located at a distance (L2) from the side wall of the tank (101) sufficiently large to allow the passage of materials in suspension contained in the spent effluents between said panels and said side wall of the tank.

16. Decanter according to one of claims 1 to 15, characterized in that the dimensions of the panels (114, 114 ') parallel to the flow of the effluents are substantially equal.

17. Decanter according to one of claims 1 to 16, characterized in that it comprises means (108) for supporting and fixing the panels (114, 114 ') to the tank (101), said means (108) being arranged in the vicinity of the upstream and downstream ends of said panels (114, 114 ').

18. Decanter according to one of claims 1 to 17, characterized in that the supply conduit (107) opens in the upper part of the upstream part of the tank (101), and forms inside the tank a elbow (108) open upstream, so as to reduce the turbulence formed by the supply of effluents.

19. Decanter according to one of claims 1 to 18, characterized in that it comprises a siphonic wall (119) disposed inside the tank (101) upstream and facing the discharge conduit (109) decanted effluents, so as to allow the retention of floating materials inside the tank (101).

20. Decanter according to one of claims 1 to 19, characterized in that the means for discharging the sludge from the decantation comprises a discharge orifice formed in the bottom (103) of the tank (101) and a conduit evacuation (111) of said sludge connected to said evacuation orifice.

21. Decanter according to one of claims 1 to 20, characterized in that it comprises, with respect to the direction of flow of the effluents, at least a first and a second series of panels (114, 114 '), said second series being located downstream of the first series, said series comprising each at least a first and a second set of at least one panel.

22. Purification plant comprising a decanter (100) according to one of the preceding claims, characterized in that it further comprises an anaerobic sludge digester (200) comprising:

- a fresh sludge supply inlet connected to the means for discharging sludge from the settling of the primary settling tank (100); - an effluent discharge outlet connected to the effluent supply inlet to be decanted from the primary decanter (100);

- a discharge outlet of the digested sludge.

23. Treatment plant according to claim 22, characterized in that it further comprises a filter (1) comprising:

- an inlet (3) of effluents to be filtered, connected to the discharge conduit (109) of the settled effluents;

- an outlet (14) for filtered effluents;

- a withdrawal outlet (22a, 22b, 22c) of the excess biomass.

24. Treatment plant according to claim 22 or 23, characterized in that the digester (200) comprises a tank (201) having a bottom (203) substantially horizontal, a supply conduit (207) of the sludge tank fresh, an outlet pipe (209) for the effluents outside the tank, and means for removing (212) the digested sludge from the tank, said tank comprising at least one wall (213a, 213b, 213c) transverse to the effluent flow, the wall defining an upstream compartment (218a, 218b, 218c) and a downstream compartment (218b, 218c, 218d) so that the tank has a first upstream compartment (218a), wherein the duct opens supply (207) of fresh sludge, and a last downstream compartment (218d), into which the effluent discharge conduit (209) opens, characterized in that the wall (213a, 213b, 213c) has, at its lower part, a communication opening (216) from the upstream compartment to the front compartment l, so as to allow passage sludge and the flow of effluents, above and through the layer of sludge maintained at the bottom of the tank, substantially horizontally from the first upstream compartment (218a) to the last downstream compartment (218d).

25. Treatment plant according to one of claims 22 to 24, characterized in that it further comprises a thickener (48) comprising:

- An input connected to the outlet for digested sludge from the digester (200);

- an outlet for thickened sludge; - an outlet for residual water connected to the inlet for the supply of effluents to be decanted from the primary decanter (100).

26. Treatment plant comprising a decanter (100) according to one of claims 1 to 21, characterized in that it further comprises a filter (1) comprising:

- an outlet (14) for filtered effluents;

- a withdrawal outlet (22a, 22b, 22c) of the excess biomass.

27. Wastewater treatment plant according to claim 23 or 26, characterized in that the filter comprises a reactor (2) wherein the effluent stream to be filtered is arranged to flow from bottom to top, said reactor (2) comprising:

- in the lower part, an inlet (3) for the effluents to be filtered and an inlet (6) for oxygenated gas;

- And, in the upper part, an outlet (14) for the filtered effluents;

- filtering means (18) comprising layers of particles of a solid material forming supports and a biomass attached to the surface of said supports, said filtering means (18) having a density less than the density of the effluents to be filtered and being interposed between the inlet (3) of the effluents to be filtered and the outlet (14) of the filtered effluents; the reactor (2) being subdivided into at least three superimposed compartments forming stages by means of at least two walls (19a, 19b, 19c) provided openings, said openings being arranged to retain the filtering means (18), so as to form in the reactor (2):

- at least two filtration stages (20a, 20b, 20c);

- And an upper outlet stage (17), the outlet (14) of the filtered effluents opening into the upper outlet stage (17); each filtration stage (20a, 20b, 20c) being provided with a layer of its own filtering means (18), and comprising, in the lower part, a withdrawal outlet (22a, 22b, 22c) of the excess biomass, the quantity and density of the filtering means (18) in each filtration stage (20a, 20b, 20c) being such that, in withdrawal mode, the lower part of at least the lower stage or stages (20a, 20b) into which opens the withdrawal outlet (22a, 22b) is free of filtering means, so as to allow the recovery of excess biomass.

28. Treatment plant according to claim 23, 26 or 27, characterized in that it further comprises a secondary settling tank (51) comprising:

- an effluent inlet to be decanted connected to the withdrawal outlets (22a, 22b, 22c) of the filter (1);

- an outlet for the decanted effluents; - means for evacuating sludge from decantation.